This invention relates to add-on armor plates, installable on the inner surfaces of "unprotected" vehicles, structures, or other craft. That is, vehicles, structures, or other craft, (such as aircraft), having walls which are not constructed of armor plate. Add-on armor plates provide additional protection to vehicle occupants and internal equipment against the risks of injury or damage due to high explosive anti tank (HEAT) rounds and kinetic energy rounds, as well as small arms fire. When a munition type projectile penetrates an unprotected wall surface of a vehicle, structure or other craft, an extremely dangerous, life-threatening situation is created, not only by the round itself but also by flying metallic debris caused by the ballistic damage to the vehicle's interior as the round penetrates. The flying, metallic debris, is known as "spall". This "spalling" effect greatly increases the risk of death or disablement of the vehicle's crew and occupants. Further, it can severely damage a vehicle's internal equipment, especially electronic and communication equipment, including computer systems which are now an integral part of many military vehicles.
The use of ballistic spall liners installed adjacent to the inner surface of a wall, roof or other vehicle structure, to control and supress the spall generated when a projectile penetrates the vehicle's interior is well known. (See for example U.S. Pat. No. 3,575,786). Ballistic spall liners, to be practical, however, must not only possess the capability to control and supress spall, but must also be designed to minimize disadvantages associated with all types of armor plate, i.e., excessive weight and, excessive thickness. To avoid these disadvantages, especially excessive weight, the use of various non-metallic materials, such as ceramic fiber and high tensile strength woven fabrics (such as polyaramid fabric and nylon) have been explored. Materials of this type yield when impacted by a projectile, thereby allowing the woven strands to act in cooperation to absorb the projectile's energy (see for example U.S. Pat. No. 2,697,054). Although the use of such non-metallic materials in ballistic spall liners has resulted to some extent in providing the advantage of reduced weight, the disadvantages of excessive spall liner thickness and high cost have remained. For example, a ballistic spall liner comprised of 34 layers of polyaramid fabric bonded together with a resinous adhesive into a class B laminate in accordance with U.S. Military specification, Number MIL-L-62474B(AT), 25 June 1984, has a ballistic limit of approximately 2400 ft/sec against a .30 caliber Fragment Simulator. While the weight of such a ballistic spall liner is acceptable at approximately 4.5 lbs/sq ft,the liner is excessively thick, at approximately 3/4", and very expensive at approximately $70/sq ft.
Non-metallic spall liners (such as a 34 ply polyaramid fabric liner) generally must be positioned a distance of approximately 12-14 inches away from the surface of an unprotected wall, in order to provide adequate ballistic protection. This unfortunately results in a great deal of trapped space which is unavailable for use. My invention, however, can be placed directly against the unprotected wall and still provide adequate ballistic protection. The best results should be obtained however if my ballistic spall liner is positioned approximately 2 inches from the inner side of the unprotected wall. Even with this 2 inches of lost, trapped space, my invention still allows significantly more untrapped space available for use, than does a spall liner made from all non-metallic materials. As such, a typical four sided structure, such as a military vehicle, may have its internal cargo and/or crew compartment increased by up to 10 to 12 additional inches of usable space in each direction by using my spall liner rather than a non-metallic spall liner.
It is an object of my invention to provide an improved ballistic spall liner usable on military vehicles, vessels, aircraft, and other structures, or as a portable shield, to provide acceptable ballistic protection at a relatively low cost without being excessively heavy or excessively thick.
It is also an object of my invention to provide ballistic spall liners of different design and composition for use on different interior wall surfaces. The design and composition of spall liners for vertical walls, which are vulnerable to the increased threat from direct fire weapons, must provide substantially better ballistic protection than spall liners for the horizontal (roof) surfaces, which are vulnerable to the lesser threat from overhead projectiles.
The aforesaid objects of the invention and other objects, which will become apparent as the description proceeds are achieved by providing a ballistic spall liner which is a laminated structure, composed of a plurality of high tensile strength, fabric layers. Each fabric layer is comprised of at least 3 plies of high tensil strength, fabric, bonded together with a resinous adhesive into a sublaminate. The laminated structure is reinforced by at least one layer of high tensil strength (minimum 220,000 p.s.i.), martensite sheet steel, interposed between the fabric layers. When a projectile penetrates the spall liner, individual plies of fabric undergo delaminating actions within a constrained area near the projectile's path. Successive layers of the spall liner begin to recede at the point of impact, forming a bulge within the interior of the liner. The steel sheets help to contain the bulge, fragment the projectile, and trap the fragments within the bulge. Unpenetrated fabric layers downstream from the steel sheet act in tension to absorb forces not contained by the steel .